Fatty acid methyl esters from soapstocks with potential use as biodiesel

Refined vegetable oils are the main feedstocks for biodiesel production presently. However, the source and price of refined vegetable oils always restrict the development of biodiesel industry in many regions. Large amount of cheap soapstocks (SSs) are currently available in oil refining process, which may provide potential feedstocks reservoir. In this paper, one technical route involving acidification, separation of free fatty acids (FFAs) and glycerides through molecular distillation, followed by esterification and transesterification, respectively, was proposed for effective conversion of SSs. The acid oil obtained from acidification of SSs was distilled at 180 °C to isolate FFAs and glycerides. Esterification was then catalyzed by solid superacid catalyst, SO42-/ZrO2–TiO2/La3+, with a methanol to oil ratio of 15:1, catalyst amount of 5 wt.% and reaction time 4 h at 60 °C. The conversion efficiency could reach 98.02%. Transesterification with glycerides was also carried out with methanol to oil molar ratio of 5:1 and catalyst (sodium methoxide) amount of 0.6% and reaction time 0.5 h at 55 °C. The conversion efficiency could reach 97.25%. Purification of transesterification products was operated at the evaporating temperature of 120 °C. The content of FAME in the distillate was above 95% analysed by gas chromatography–mass spectrometry (GC–MS).